Scale is a slightly soluble inorganic salt, such as barium or strontium sulfate, calcium carbonate, calcium sulfate or calcium fluoride. In the oil production from the subterranean formations, the deposition of scale on surfaces and production equipment is a major production problem. Scale build-up decreases permeability of the formation, reduces well productivity and shortens the lifetime of production equipment. In order to clean scaled-up wells and equipment it is necessary to stop the production, i.e., by killing the well which is time-consuming and costly. After killing the well, squeezing is performed by injecting scale inhibitors into the well. Squeezing is therefore done after stimulation, e.g., mechanical fracturing, and requires the well production to be stopped. In a typical squeezing operation, fully dissolved scale inhibitor is pumped into the well and left to percolate for a period of 24 hours or longer. The scale inhibitor then either is consumed in the scale inhibition process or flows back out of the well as the well is again allowed to produce oil. In another approach, a continuous injection of liquid inhibitor via a pump into the well annulus, which is then pumped into the well bore near the production perforation. This technique only treats production fluid in the well bore.
Organic-based crystalline build up, such as paraffin and asphaltene, causes issues similar to those caused by scale build up. Similarly, in order to clean the organic-based crystalline build up, the well must be killed and squeezed as described above.
Previous solutions to the problem of reducing the cost and trouble of scale inhibitor squeeze operations, and in particular, the faster than desired depletion of scale inhibitor from subterranean formations have included squeezing cross-linked scale inhibitor gels or nanoparticles into a subterranean formation to moderately lengthen the effective life of the treatment and suspending very small cross-linked particles for percolation through subterranean formations. These nanoparticles were from 100 nanometer to less than 10 micron in size. These processes however negatively impact the formations since the gels and nanoparticles reduce the permeability of the rock formations and cause formation damage. Another solution includes a polymeric particle with covalently bound well treatment chemicals, however, this solution does not provide any particles comprising a functional cross-linked scale control agent and does not provide controlled release scale control. Other solutions have included particles for use in a frac operation together with standard high crush-resistant proppant particles in which the particles consist of porous high strength ceramic beads which are impregnated with scale inhibitor for inclusion. These particles, however, can only be loaded with a low level of scale inhibitor and because the scale inhibitor is only bound by physical forces within the pores of the ceramic bead, it is released much faster especially at high temperatures.
Yet another solution included a fluid suspension that contains a mixture of a particulate, a tackifying compound and a treatment chemical. The tackifying compound causes the treatment chemical to be stuck in the oilwell formation. Yet another solution included a scale inhibitor or a corrosion inhibitor in the form of particles that are coated, for example, with a dispersing agent.
However, there is still a need for controlled release scale control agent particles that have a high load of scale control agent controlled release and that could be used in a frac operation so that squeezing frequency needs could be dramatically reduced and oil producing wells could produce for much longer durations without having to be shut down for scale removal.